There are many cases where it is necessary to supplement liquid such as a raw material which decreases by operation or use of an equipment or apparatus. In such cases, supply of liquid such as a raw material is made by coupling a cartridge container to a container provided on the side of a main body of an equipment or apparatus for shifting the liquid between the two containers or by exchanging a container provided on the main body with another container.
Various detachable types of couplers are used for simply performing such coupling or exchanging between two containers.
For example, Japanese Patent Application Laid-open Publication No. 2003-172487 discloses in its FIG. 9 a coupling device which consists of a plug P having a main flow path and a sub-flow path and a socket S having a main flow path and a sub-flow path and being connectable to the plug and being capable of communicating with the main flow path and the sub-flow path of the plug in a coupled state.
According to this coupling device, the socket S comprises a main flow-path 2a formed outside of the outer periphery of a valve pusher 2 fixed to a holder 1, a sub-flow path 2b formed further outside of the main flow path 2a, and valves 3a and 3b for closing the flow paths 2a and 2b. The respective valves 3a and 3b are pushed toward their valve seats by energizing force of springs 4a and 4b to close the main flow path 2a and the sub-flow path 2b. 
The plug P comprises a main flow path 6a formed outside of the periphery of a valve main body 6 held slidably by a valve holder 5, a sub-flow path 6b formed outside of the main flow path 6a, and valves 7a and 7b for closing the flow paths 6a and 6b. The respective valves 7a and 7b are pushed toward their valve seats by energizing force of springs 8a and 8b to close the main flow path 6a and the sub-flow path 6b. 
When the socket S is connected to the plug P, the sub-valve 3b of the socket S abuts against the sub-valve 7b of the plug P and these valves 3b and 7b are displaced in a direction to separating apart from each other against the force of the springs 4b and 8b thereby causing the sub-flow paths 2b and 6b to communicate with each other.
As the socket S is further connected to the plug P, the main valve 3a of the socket S is pushed by the end surface of an inner cylinder of the plug P to withdraw from the valve seat of the valve pusher 2 against the force of the spring 4a and thereby open the main flow path 2a relative to the valve pusher 2. Simultaneously, the end surface of the valve pusher of the socket S abuts against the surface of the valve provided on the valve main body 6 of the plug P and thereby the valve main body 6 of the plug P is pushed against the force of the spring 8a to cause the valve main body 6 to retreat and thereby open the main valve 7a to communicate with the main flow path 6a. 
By this arrangement, when the sub-flow path is communicated, gas is supplied from a gas supply source to the inside of the container and an inner bag provided in the container is contracted to supply liquid in the inner bag from the main flow path of the plug to the outside of the container through the main flow path of the socket.
Various liquid type fuel cells which can generate electricity directly from liquid fuel have recently been developed. A direct methanol fuel cell (DMFC) which uses methanol as its fuel has drawn attention as for its use as a power source of portable type electronic devices, for it can be made compact without using a reforming device.
Particularly, in a passive type direct methanol fuel cell (DMFC), methanol is supplemented directly by coupling a fuel cartridge containing methanol which is liquid fuel to a fuel tank provided on the side of a fuel cell main body whereby a pump for supplying fuel becomes unnecessary and the fuel cell can be made further compact (Japanese Patent Application Laid-open Publication No. 2005-71713).
In an active type fuel cell, a pump mechanism is provided on the side of a fuel cell main body and the fuel cell is coupled to a fuel cartridge containing methanol and methanol is pumped out of the fuel cartridge by the pump mechanism and supplied to a fuel tank.
In both types of the methanol fuel cells, various methanol aqueous solutions as well as pure methanol of different concentrations are used as methanol as the fuel. Further, in some fuel cells, not only methanol fuel but also ethanol fuel such as ethanol aqueous solutions and pure ethanol and also other fuels including dimethyl ether and formic acid are used.